Local area networks (“LAN”) have enabled digital networking of almost any computing device, including, computers, laptops, personal digital assistants, scanners and any other devices that deal with digital information. However, traditionally, the physical reach of LANs has been limited because they require a physical or hardwired connection between computing devices. Even with phone dial-ups, a LAN network is ultimately limited by its hard-wired nature. To overcome this limitation, wireless solutions were developed.
In a wireless LAN (“WLAN”), network connections are accomplished by use of a wireless technology such as radio frequency (“RF”), infra-red, microwave, millimeter wave or other type of wireless communication instead of cable. This allows a computing device to remain connected to the network while it is mobile or while it is not physically connected to the WLAN. The connection is usually accomplished and maintained through the use of an interface card installed in the computing device. WLANs may also include connections to a wired network, such as a LAN. Connections to the wired network are accomplished through the use of access points. Access points are connected to a node using some type of wired connection. An access point can reside at any node on the wired network and acts as a gateway for routing data (“IP traffic”) between the wired and wireless portions of the network.
Several protocols have been proposed to standardize WLANs to allow greater compatibility with a wide range of devices, networks and components. One such protocol is the IEEE 802.11. The IEEE 802.11 protocol specifies both the architectures and layers of a WLAN. The IEEE 802.11 protocol specifies the physical and medium access control (“MAC”) layers of a WLAN. The physical layer handles the wireless transmission of data, and is generally a form of RF or infrared communication. The MAC layer is a set of protocols which is responsible for maintaining order.
With regard to architecture, the IEEE 802.11 protocol specifies two types. The first, shown in FIG. 1, is the ad hoc network. The ad hoc network can be spontaneously created with a plurality of computing devices. As shown in FIG. 1, the ad hoc network has no structure, no fixed points and generally, every computing device can communicate with every other computing device. The second type of architecture is the infrastructure. As shown in FIG. 2, this architecture uses access points through which the computing devices can communicate with each other and a node of a wired network (hereinafter “node”). Computing devices communicate with an access point through some type of wireless technology and the access points communicate with a node through some type of wired technology. Nodes can communicate with each other through various types of networks, such as the Internet, generally by some type of wired connection. A distribution system, which is the mechanism by which the access points communicate with each other, is included in the access points, and also includes the Nodes, networks, and the connections among them. Each access point has a range over which it provides service. Each of these ranges is a basic service set (“BSS”); while the BSS and the distribution system form an extended service set (“ESS”) which defines the range over which services can be provided. The location of the computing device on the network is determined by the access point to which it is connected.
A computing device can move about within the range of the access point to which it is connected. If the WLAN is designed so that there is some overlap of the ranges of the access points, it may be possible for a computing device to move among the access points and remain connected to the WLAN and continue to send and receive IP traffic. In order to do this, the WLAN needs to know where the computing device is so that it knows where to direct IP traffic intended for the computing device. In other words, the WLAN must track the computing device.
Generally, in order for the network to track the computing device, the computing device associates with an access point at a given time interval, upon its movement or when the computing device travels between or among the ranges of different access points. IP traffic intended for the computing device is forwarded to the last access point with which the computing device had associated and then forwards the IP traffic to the computing device. However, tracking and forwarding IP traffic to the computing device in this manner can lead to a power drain on the computing device and a high level of signaling over the network. For example, if the computing device must associate with a new access point whenever it enters the range of the new access point, the computing device must remain on at all times so that it may detect when it has entered the range of the new access point. Additionally, the computing device must remain on at all times to receive any incoming IP traffic. This continuous detection and repeated associating causes a tremendous drain on the computing device's power supply and adds to the signaling across the network.
To overcome these disadvantages, the IEEE 802.11 protocol includes dormant mode functionality. Dormant mode functionality (without paging functionality) allows a computing device to operate in two modes, an “active” mode and a “dormant” mode. In the active mode, the computing device can receive signals, such as IP traffic, and can send signals such as those sent when the computing device associates with an access point. In the dormant mode, the computing device is not turned off, but is put into a mode which reduces its ability to receive IP traffic by reducing the monitoring of certain channels and thus is a state of reduced power consumption. The computing device must be in active mode to send or receive IP traffic and associate with an access point. Therefore, the computing device must periodically go into active mode to associate with an access point and to send or receive IP traffic. Because IP traffic intended for the computing device may be transmitted while the computing device is in dormant mode, the IEEE 802.11 protocol incorporates buffers in the access points to queue IP traffic intended for the computing device. The computing device can then receive this IP traffic when it switches into active mode and therefore does not miss any IP traffic sent while it was in dormant mode. Although dormant mode functionality does provide some power savings for the computing device and reduced signaling across the network, the computing device must still periodically switch into active mode to register with each access point of which it is in range, and to send or receive IP traffic.
Further reductions in computing device power drain and signaling across the network can be accomplished through the use of paging. Paging is a method of notifying a dormant computing device of incoming IP traffic. Paging includes (i) the use of paging areas; and (ii) paging the computing device. The use of paging areas includes the creation of paging areas and having the computing device signal the network only when it crosses a paging area boundary. A paging area boundary is defined by the outer perimeter of the ranges of a collection of access points (an “access point group”) that are used to locate a dormant computing device. This outer perimeter forms the paging area boundary of a paging area. Each paging area uniquely identifies itself to computing devices by periodically broadcasting that paging area's unique paging area identifier.
Generally, a network implementing paging will be arranged to have at least two paging areas. Only when a computing device crosses a paging area boundary from one paging area to another, does the computing device associate with the nearest access point. A computing device detects when it crosses a paging area boundary by detecting a change in the unique paging area identifier. However, because neighboring paging areas usually overlap with each other to prevent gaps in coverage, a computing device may be in more than one paging area simultaneously and thus will detect more than one paging area identifier. In this case, the computing device will detect the strength of the paging area identifier from each paging area that computing device is within and will associate with the paging area from which the strongest paging area identifier is broadcast.
The computing device is programmed to periodically go from dormant to active mode so that it may detect the unique paging identifier or identifiers being broadcast. By requiring a computing device to associate with the network only when it crosses a paging area boundary, the amount of signaling to the network is decreased and the amount of time the computing device can remain dormant is increased, thus power consumption is decreased. Further reduction in power usage and signaling by the computing device is realized because the computing device only periodically needs to switch into active mode.
One of the consequences of reducing the number of instances in which the computing device informs the network of its location in the previously-described manner is that the network does not know the location of the computing device within a given paging area. Because the computing device may have moved after the last time it associated with an access point, all that the network knows is that the computing device is located somewhere within the paging area in which the access point with which the computing device last associated is located (the “old access point”). In order for the network to forward IP traffic to the computing device, it must know the access point for which the computing device is currently in range (the “new access point”) and alert the computing device about the pending IP traffic. The network precisely locates the computing device within a paging area by paging the computing device. Paging the computing device is signaling by the network through the access points directed to locating the computing device and alerting it to establish a connection. Paging the computing device involves transmitting a request to all the access points in the same paging area as the old access point. These access points then broadcast the paging signal. When the computing device receives the paging signal it associates with the new access point. Once the computing device associates with the new access point, the network knows the location of the computing device in terms of the access point in which it is in range. The new access point then signals the old access point, the old access point sends any buffered IP traffic to the new access point and the new access point delivers the buffered IP traffic to the computing device. Power drain on the computing device and signaling over the network are reduced because the computing device only associates with a new access point in the same paging area when the computing device is paged.
Although many cellular-based wireless WAN protocols support paging, WLAN protocols, such as the IEEE 802.11, do not specifically provide standards or methods for implementing paging. For example, the IEEE 802.11 protocol does not have paging areas, a dedicated paging channel and a radio link protocol specifically directed towards locating a dormant computing device. Additionally, the IEEE 802.11 and other WLAN protocols lack the protocols for establishing and altering paging areas, associating a computing device with an access point, and performing paging. Furthermore, existing WLAN protocols do not address the issues of maintaining synchronization of the access points across each access point group and reducing signal interference among access points.
The advantages of the methods and apparatuses disclosed herein will be apparent from the following summary and detailed description of the preferred embodiments.